1. Field of the Invention
The present invention relates to a combined cycle power plant using fossil fuel including methanol and the like.
2. Description of the Prior Art
FIG. 28 is a diagrammatic view of a prior art combined cycle power plant, using pure oxygen as oxidizing agent and methane as fuel, which has been disclosed from the Graz Institute of Technology. In the figure, numeral 1 designates a compressor, which compresses a mixture gas of steam and carbon dioxide as working fluid to a pressure decided by an entire system optimization study. Numeral 2 designates a combustor, which is supplied with oxygen needed for an equivalent combustion of the methane as fuel to generate a high temperature high pressure combustion gas, wherein components of the combustion gas are carbon dioxide and steam. Numeral 3 designates a high temperature gas turbine, which expands the high temperature high pressure combustion gas to obtain a work. Numerals 4, 5 designate first and second heat exchangers, respectively, and a condensed water produced at a bottoming system from an exhaust gas of the high temperature gas turbine 3 extracted at a midpoint between the first and second heat exchangers 4, 5 is heated at the first and second heat exchangers 4, 5 to generate a high temperature high pressure steam. Numeral 6 designates a high pressure steam turbine, which expands the high temperature high pressure steam generated at the first and second heat exchangers 4, 5 approximately to an inlet pressure of the combustor 2 to obtain a work as well as to send the steam so expanded to be mixed into an inlet of the combustor 2. Remaining exhaust steam from the high temperature gas turbine 3 which has passed through the first and second heat exchangers 4, 5 with its temperature having been reduced returns to an inlet of the compressor 1.
Numeral 7 designates a low pressure turbine, which expands the combustion gas extracted at the midpoint between the first and second heat exchangers 4, 5 approximately to a vacuum to obtain a work. Numeral 8 designates a carbon dioxide compressor (vacuum pump), which compresses the mixture gas the containing the entire amount of the carbon dioxide generated at the combustor 2 approximately to the atmospheric pressure to thereby discharge the carbon dioxide as a combustion-generated product outside of the system. Numeral 9 designates a condenser, in which an outlet gas of the low pressure turbine 7 which has been pressure-reduced by the carbon dioxide compressor (vacuum pump) 8 is heat-exchanged by the sea water or the like to be temperature-reduced so that the steam is liquefied. The liquefied water is pressurized by a pressure pump 10 to be fed into the first and second heat exchangers 4, 5 to thereby become the high temperature high pressure steam. The steam as the combustion-generated product which has been expanded at the low pressure turbine 7 is mostly liquefied to water at the condenser 9, and a remaining portion thereof becomes a drain in the process of being compressed by the vacuum pump 8 approximately to the atmospheric pressure to be discharged outside of the system.
In the prior art combined cycle power plant as mentioned above, while the high temperature combustion gas having the component of carbon dioxide and steam is obtained using the methane as fuel and oxygen, it is also possible to use a methanol (CH.sub.3 OH) fuel or other fossil fuels, but in this case, it has been a problem that the gross thermal efficiency is low.